Methods of manufacturing abrasive particle and polishing slurry

ABSTRACT

Provided is a method of manufacturing an abrasive particle including a mother particle and a plurality of auxiliary particles formed on a surface of the mother particle, and a method of manufacturing a polishing slurry in which the abrasive particle is mixed with a polishing accelerating agent and a pH adjusting agent.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/483,140, filed Sep. 10, 2014, which claims priority to Korean PatentApplication No. 10-2013-0109872 filed on Sep. 12, 2013 and all thebenefits accruing therefrom under 35 U.S.C. §119, the contents of whichare incorporated by reference in their entirety.

BACKGROUND

The present disclosure relates to a method of manufacturing an abrasiveparticle, and more particularly, to methods of manufacturing an abrasiveparticle and a polishing slurry capable of enhancing the polishing rateof a target layer to be polished and decreasing micro scratches.

A chemical mechanical polishing (CMP) process is conducted by apolishing pad equipped in a polishing apparatus after a slurrycontaining abrasive particles is put on a substrate. In this regard, theabrasive particles mechanically polish a surface of the substrate with apressure applied from the polishing apparatus, and chemical componentscontained in the slurry chemically react with the surface of thesubstrate to chemically remove a portion of the surface of thesubstrate. The abrasive particles may include, for example, ceria(CeO₂), and the like, and may be selectively used according to targetlayers to be polished.

Meanwhile, in existing methods of manufacturing a NAND flash memory, theshallow trench isolation (STI) process in which a nitride layer is usedas a hard mask in order to form a device isolation layer is conducted.That is, a nitride layer is first formed on a substrate, a trench isformed on a predetermined region of the substrate, an oxide layer isformed to fill the trench, and the oxide layer is polished to form adevice isolation layer. In this regard, the oxide is polished using adry ceria slurry capable of securing a high polishing selection ratio ofthe oxide layer and the nitride layer until the nitride layer isexposed, and then the remaining nitride layer is removed by a wetetching. However, when the device scale is reduced to 20 nm or less,loss of the oxide layer occurs during the wet etching of the nitridelayer and leakage current sharply increases between devices due to theloss of the oxide layer, so that the devices may be erroneouslyoperated.

To solve the above-described problems, a new CMP process has beendeveloped, which uses a polysilicon layer used as a floating gate as apolishing stop layer instead of using the nitride layer as a hard mask.That is, a tunnel insulating layer and a polysilicon layer are formed ona substrate, the polysilicon layer, the tunnel insulating layer and thesubstrate are sequentially etched to form a trench, an insulating layeris formed to fill the trench, and then the insulating layer is polisheduntil the polysilicon layer is exposed, thereby forming a deviceisolation layer. Herein, when surface defects, particularly, microscratches are generated in the polysilicon layer used as a floating gateafter the CMP process, the generated micro scratches have an influenceon the threshold voltage of devices. Then, since the dry ceria particleshave an angular grain shape and a wide grain size distribution as shownin FIG. 1 due to limitations of the manufacturing method, theapplication of such dry ceria particles to the CMP process for formingNAND flash memory devices inevitably creates micro scratches. Comparedwith the dry ceria particles, since wet ceria particles have arelatively narrow grain size distribution, do not create particleshaving a large secondary particle diameter, and have a polyhedralstructure as shown in FIG. 2, the wet ceria particles may greatlyimprove micro scratches compared with the dry ceria particles. However,when the size of the wet ceria particles is not larger than 40 nm, thepolishing rate of the insulating layer is very low, and the size of thewet ceria particles is 100 nm or larger, the number of micro scratchesis sharply increased due to sharp crystal faces of the polyhedralstructure.

Meanwhile, U.S. Pat. Nos. 6,221,118 and 6,343,976 disclose a method ofsynthesizing a ceria particle used for polishing an insulating layer ina shallow trench isolation (STI) process, and a substrate polishingmethod using the same. The related arts also disclose an averageparticle diameter and a particle diameter distribution range of abrasiveparticles required for the characteristics of a slurry for polishing aninsulating layer. However, since the ceria particles disclosed in theabove-described related arts substantially include macro abrasiveparticles causing micro scratches, the ceria particles fail to suppresscreation of micro scratches.

SUMMARY

The present disclosure provides methods of manufacturing an abrasiveparticle and a polishing slurry capable of enhancing the polishing ratioof a target layer to be polished and minimizing micro scratches.

The present disclosure also provides an abrasive particle and apolishing slurry capable of enhancing the polishing ratio of a targetlayer to be polished and minimizing micro scratches by decreasing sharpcrystal faces of the abrasive particle having a polyhedral structure tothe maximum extent.

The present disclosure also provides a method of manufacturing anabrasive particle capable of reducing sharp crystal faces by formingprojection-shaped auxiliary particles on surfaces thereof having apolyhedral structure, and a polishing slurry.

In accordance with an exemplary embodiment, a method of manufacturing anabrasive particle, includes: mixing a first precursor material aqueoussolution and a diluted alkaline solution and thermally treating themixture solution to prepare a mother particle having a polyhedralcrystal face; and adding an alkaline solution to a mixture solution inwhich the mother particle is mixed, mixing a second precursor materialaqueous solution and thermally treating the resultant mixture solutionto form a plurality of auxiliary particles protruded outward from asurface of the mother particle.

The plurality of auxiliary particles may be formed so as to cover aportion of each of crystal faces centered on an edge portion where atleast three crystal faces among the polyhedral crystal faces meet.

The preparing of the mother particle may include: mixing a precursormaterial with deionized water to prepare the first precursor materialaqueous solution; preparing a diluted alkaline solution and loading andstirring the prepared alkaline solution in a reaction container; mixingthe first precursor material aqueous solution in the reaction containerand thermal treating the resultant mixture solution; and cooling thethermally treated mixture solution.

The above method may further include mixing an acidic solution to thefirst precursor material aqueous solution.

The thermally treating may be conducted at a temperature higher than 60°C. and not higher than 100° C. for approximately 2 hours toapproximately 24 hours.

The thermally treating temperature may rise at a rate of approximately0.2° C./min to approximately 1° C./min.

The forming of the auxiliary particles may include: adding and stirringan alkaline solution in a mixture solution in which the mother particleis mixed; mixing the second precursor material aqueous solution preparedby mixing a precursor material with deionized water in the mixturesolution in which the mother particle is mixed; thermally treating themixture solution; and cooling the thermally treated mixture solution.

The thermally treating may be conducted at a temperature higher than 60°C. and not higher than 100° C. for approximately 2 hours toapproximately 24 hours.

The thermally treating temperature may rise at a rate of approximately0.2° C./min to approximately 1° C./min.

The above method may further include repeating the adjusting of the sizeof the auxiliary particles at least one time.

The adjusting of the size of the auxiliary particles may include: addingand stirring an alkaline solution in a mixture solution in which anabrasive particle including the mother particle and the auxiliaryparticles formed on the surface of the mother particle is mixed; mixinga third precursor material aqueous solution prepared by mixing aprecursor material with deionized water in the mixture solution in whichthe abrasive particle is mixed; thermally treating the mixture solution;and cooling the thermally treated mixture solution.

The thermally treating may be conducted at a temperature higher than 60°C. and not higher than 100° C. for approximately 2 hours toapproximately 24 hours.

The thermally treating temperature may rise at a rate of approximately0.2° C./min to approximately 1° C./min.

The auxiliary particles adjacent to each other may be spaced apart fromeach other or contact each other.

The plurality of auxiliary particles contacting each other may have anoverlapping height ranging from approximately 0% to approximately 70% toa maximum height thereof.

Each of the mother particle and the auxiliary particles may include aceria particle.

The auxiliary particle to the mother particle may be formed at a sizeratio of approximately 100:1 to approximately 5:1.

The abrasive particle may be formed to have an average particle diameterranging from approximately 6 nm to approximately 350 nm.

The mother particle may have an average particle diameter ofapproximately 5 nm to approximately 300 nm and the auxiliary particlemay have an average particle diameter of approximately 1 nm toapproximately 50 nm.

In accordance with another exemplary embodiment, a method ofmanufacturing a polishing slurry polishing a workpiece, wherein anabrasive particle which polishes the workpiece and has a plurality ofprotrusions protruded outward is dispersed in a dispersing agent.

The abrasive particle may include polyhedral crystal faces, and theprotrusion may be formed from an edge where at least two of thepolyhedral crystal faces meet.

The auxiliary particle to the mother particle may be formed at a sizeratio of approximately 100:1 to approximately 5:1.

The abrasive particle may be contained in an amount ranging fromapproximately 0.1 wt % to approximately 5 wt % based on a solidcomponent.

The above method may further include adding a polishing acceleratingagent, wherein the polishing accelerating agent may include a cationiclow molecular weight polymer, a cationic high molecular weight polymer,a hydroxylic acid, and an amino acid, which convert a surface potentialof the abrasive particle to a minus potential.

The polishing accelerating agent may be contained in an amount ofapproximately 0.01 wt % to approximately 0.1 wt % based on 1 wt % of theabrasive particle.

The cationic low molecular and high molecular polymers may include atleast one of an oxalic acid, a citric acid, a polysulfonic acid, apolyacrylic acid, a polymethacrylic acid (Darvan C-N), copolymeric acidsthereof, or salts thereof, the hydroxylic acid comprises at least one ofa hydroxylbenzoic acid, an ascorbic acid, or salts thereof, and theamino acid comprises at least one of a picolinic acid, a glutaminicacid, a tryptophan acid, an aminobutylic acid, or salts thereof.

The above method may further include adding a pH adjusting agentadjusting pH of the slurry, wherein the pH of the slurry is maintainedin a range of 4 to 9 by the pH adjusting agent.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments can be understood in more detail from thefollowing description taken in conjunction with the accompanyingdrawings, in which:

FIGS. 1 and 2 show photographs of existing dry and wet ceria abrasiveparticles and schematic views of polishing using these particles;

FIG. 3 is a schematic view of abrasive particles according to anembodiment of the present disclosure;

FIG. 4 is an enlarged schematic view of an abrasive particle in whichadjacent auxiliary particles overlap;

FIGS. 5 and 6 are a flow diagram and a heat treatment condition diagramfor explaining methods of manufacturing an abrasive particle accordingto embodiments of the present disclosure;

FIGS. 7 to 9 are schematic views and photographs of abrasive particlesobtained by a manufacturing method according to an embodiment of thepresent disclosure;

FIG. 10 is photographs for comparison between existing dry and wetabrasive particles and abrasive particles of the present disclosure;

FIG. 11 shows a photograph of abrasive particles according to thepresent disclosure and a schematic view of polishing using the abrasiveparticles;

FIG. 12 is an XRD graph of existing dry and wet abrasive particles andabrasive particles of the present disclosure;

FIGS. 13 and 14 are a graph and a photograph showing a size distributionof auxiliary particles according to temperature in the course oftemperature rise to a heat treatment temperature of the presentdisclosure;

FIGS. 15 to 17 are a graph and a photograph showing a size distributionof auxiliary particles according to heat treatment temperature of thepresent disclosure;

FIGS. 18 to 20 are cross-sectional views illustrating a method ofmanufacturing a semiconductor device by using a polishing slurrycontaining abrasive particles according to an embodiment of the presentdisclosure;

FIGS. 21 and 22 are photographs of abrasive particles according tocomparative examples and inventive examples;

FIG. 23 is a graph showing a particle diameter distribution of abrasiveparticles manufactured according to Inventive Examples;

FIGS. 24 and 25 are photographs of sections of substrates after thesubstrates are subject to CMP processes by using slurries containingabrasive particles according to a comparative example and an example ofthe present disclosure; and

FIGS. 26 and 27 are photographs of surfaces of polishing stop layersafter substrates are subject to CMP processes by using slurriescontaining abrasive particles according to Comparative Example andInventive Example.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, exemplary embodiments will be described in detail withreference to the accompanying drawings. The present disclosure may,however, be embodied in many different forms and should not be construedas being limited to the embodiments set forth herein; rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the concept of the invention to thoseskilled in the art. Further, the present disclosure is only defined byscopes of claims.

FIG. 3 is a schematic view of abrasive particles according to anembodiment of the present disclosure;

Referring to FIG. 3, an abrasive particle according to an embodiment ofthe present disclosure includes a mother particle 10, and a plurality ofauxiliary particles 20 provided to a surface of the mother particle 10.

The mother particle 10 may include particles, such as ceria (CeO₂), andthe like. Also, the mother particle 10 may be analyzed through an XRDmeasurement, and has the same crystal structure as the wet ceria and haspolyhedral crystal faces. Also, the mother particle 10 may be providedin an average particle diameter ranging from 5 nm to 300 nm, preferablyranging from 20 nm to 100 nm, and more preferably ranging from 40 nm to70 nm. When the average particle diameter of the mother particle 10 isso small, the target layer to be polished is not easily polished so thatthe polishing rate is reduced, and when the average particle diameter ofthe mother particle 10 is so large, the mother particle 10 is againgrown up to a polyhedral structure to generate micro scratches in thepolishing stop layer. Therefore, the mother particle 10 may have anaverage particle diameter in such a range that does not reduce thepolishing rate of the target layer to be polished and does not generatemicro scratches in the polishing stop layer.

The auxiliary particle 20 is formed in plurality on a surface of themother particle 10, and may be formed protruding outward from aplurality of edge portions of the mother particle 10. That is, theauxiliary particles 20 may be formed so as to cover at least a portionof each crystal face from an edge portion where at least three crystalfaces meet. The auxiliary particle 20 may include ceria (CeO₂), and thelike. That is, the auxiliary particle 20 may be formed of the samematerial as the mother particle 10, or a material that is not the sameas the mother particle 10, and it is preferable that the auxiliaryparticle 20 be formed of the same material as the mother particle 10. Inthis regard, the auxiliary particles 20 may be grown in various sizesdepending on the growing conditions, such as the size of the motherparticle 10, growing time, growing temperature, and the like, and theadjacent auxiliary particles 20 may be formed spaced apart from eachother as shown in FIG. 3A or contacting each other as shown in FIG. 3B.Also, in case the auxiliary particles 20 contact each other, theauxiliary particles 20 are grown up on faces between edges of the motherparticle 10 according to the growing time of the auxiliary particles 20,so that the adjacent auxiliary particles 20 may overlap each other. Inthis regard, in case the adjacent auxiliary particles 20 overlap eachother, the overlapping portions of the auxiliary particles 20 are formedwith a height (d2) greater than 0 and less than 70 when it is assumedthat the maximum height (d1) of the auxiliary particles 20 is 100 asshown in FIG. 4. That is, the overlapping portions of the auxiliaryparticles 20 may be formed with a height between 0 and 70% with respectto the maximum height of the auxiliary particles 20 which is thefarthest distance of the auxiliary particles 20 from the surface of themother particle 10. In this regard, when the overlapping portions of theauxiliary particles 20 are too high, the abrasive particle becomes toolarge and is again grown up to a polyhedral structure, so that theabrasive particle may cause occurrence of micro scratch in the polishingstop layer. Meanwhile, these auxiliary particles 20 may be formed in asize ratio ranging from 1:300 to 1:5 with respect to the size of themother particle 10. For example, when the mother particle 10 is providedwith an average particle diameter ranging from 5 nm to 300 nm, theauxiliary particles 20 may be provided with an average particle diameterranging from 1 nm to 50 nm, preferably from 3 nm to 20 nm, and morepreferably from 5 nm to 10 nm. That is, the particle diameter of oneauxiliary particle 20 may be defined as a distance from the surface ofthe mother particle 10 to the farthest distance of the correspondingauxiliary particle 20, and the average particle diameter of theauxiliary particles 20 defined thus may be provided in a range of 1 nmto 50 nm. Then, when the average particle diameter of the auxiliaryparticles 20 is too small, the auxiliary particles 20 fail to reduce thesharpness of the crystal faces of the mother particle 10 and thus failto prevent occurrence of micro scratches in the polishing stop layer,and when the average particle diameter of the auxiliary particles 20 istoo large, the auxiliary particles 20 are again grown up to a polyhedralstructure surrounding the mother particle 10, so that the auxiliaryparticles 20 may cause occurrence of micro scratches in the polishingstop layer. Accordingly, the abrasive particle according to anembodiment of the present disclosure may be provided with an averageparticle diameter from one auxiliary particle 20 to another auxiliaryparticle 20 through the mother particle 10 ranging from 6 nm to 350 nm,preferably from 20 nm to 150 nm, and more preferably from 40 nm to 80nm. That is, the distance between the auxiliary particles 20 that arefarthest away from each other through the mother particle 10 may be in arange of 6 nm to 350 nm.

Methods of manufacturing an abrasive particle according embodiments ofthe present disclosure will be described with reference to FIGS. 5 and6. FIG. 5 is a flow diagram showing methods of manufacturing an abrasiveparticle according to embodiments of the present disclosure, and FIG. 6is a conditional view of heat treatment time and temperature. Also,FIGS. 7 and 9 are schematic views and photographs of abrasive particlesobtained by a manufacturing method according to an embodiment of thepresent disclosure.

Referring to FIGS. 5 and 6, a method of manufacturing an abrasiveparticle according to an embodiment of the present disclosure mayinclude preparing (S100) a mother particle, and forming (S200) auxiliaryparticles on a surface of the mother particle. The method ofmanufacturing an abrasive particle may further include increasing (S300)the size of the auxiliary particles. While the abrasive particle inrelated arts is manufactured by a solid phase reaction method and isthen pulverized to a proper size for the use thereof, the abrasiveparticle according to an embodiment of the present disclosure ismanufactured by a wet chemical synthesis method.

Hereinbelow, the forming (S100) of preparing a mother particle will bedescribed. First, a precursor, for example, a cerium aqueous solution isprepared by mixing a cerium salt with deionized water. The cerium saltand the deionized water may be mixed at a ratio of, for example, 2:1 to4:1. The cerium salt used herein may be at least one of Ce(III) salt andCe(IV) salt. That is, at least one Ce(III) salt may be mixed withdeionized water, at least one Ce(IV) salt may be mixed with deionizedwater, or Ce(III) salt and Ce(IV) salt may be mixed with deionizedwater. The Ce(III) salt may include cerium chloride, cerium bromide,cerium nitrate, acetate cerium chloride, and the like, and the Ce(IV)salt may include cerium ammonium nitrate, cerium sulfate, and the like.Preferably, the Ce(III) salt may be cerium nitrate, and the Ce(IV) saltmay be cerium ammonium nitrate. Meanwhile, in order to stabilize thecerium aqueous solution prepared by mixing cerium salt with deionizedwater, an acid solution may be mixed. The acid solution and the ceriumaqueous solution may be mixed at a ratio of 1:1 to 1:100. The acidsolution may include oxygenated water, a nitric acid, an acetic acid, ahydrochloric acid, a sulfuric acid, and the like. The pH of the ceriumaqueous solution mixed with the acidic solution may be adjusted to, forexample, 0.01. Separately from the cerium aqueous solution, an alkalinesolution is prepared. The alkaline solution may be prepared by mixingammonia, sodium hydrate, potassium hydrate, or the like with deionizedwater and diluting the mixture to a proper concentration. In thisregard, the alkaline material and deionized water may be diluted at aratio of 1:1 to 1:100, and the pH of the mixture solution may be, forexample, 12.3. The alkaline solution diluted thus is loaded in areaction container and then stirred, for example, for a time not morethan 5 hours in an atmosphere of inert gas, such as nitrogen, argon,helium, or the like. The cerium aqueous solution is added in thereaction container in which the diluted alkaline solution is loaded andis mixed with the alkaline solution, for example, at a rate of 0.1 l persecond. At this time, the pH of the mixture solution may be, forexample, 9.58. Then, the mixture solution is thermally treated at apredetermined temperature. The thermal treatment temperature may be 100°C. or lower—for example, a temperature exceeding 60° C. and not higherthan 100° C., and the heat treatment time may be 24 hours or less—forexample, 1 hour to 24 hours. Also, the temperature rise rate from roomtemperature to the thermal treatment temperature may be in a range of0.2° C./min to 1° C./min—for example, 0.5° C./min. The mixture solutionwhich has undergone the heat treatment is cooled to 60° C. or lower, forexample, within 2 hours. Through the above processes, a mixture solutionin which the mother particle 10 having a particle diameter of 80 nm orless is mixed is prepared. That is, the mother particle is formed in apolyhedral structure having sharp crystal faces without any auxiliaryparticles on a surface thereof as shown in the schematic view of FIG. 7Aand the photograph of FIG. 7B.

Next, the growing (S200) of auxiliary particles on a surface of themother particle will be described. In a state that the atmosphere ofinert gas is maintained, the alkaline solution is further added in themixture solution in which the mother particle 10 is mixed and thenstirring is performed for a time of 5 hours or less. In this regard, thealkaline solution may be, for example, ammonia that is not diluted bydeionized water. A cerium aqueous solution prepared by mixing ceriumsalt with deionized water at a mixing ratio of 2:1 to 4:1 is mixed withthe mixture solution in which the mother particle 10 is mixed, and theresultant solution is then heated at a temperature of 100° C. or lower,for example, at a temperature exceeding 60° C. and not higher than 100°C. to perform heat treatment for a time of 24 hours or less. In thisregard, the temperature of the mixture solution may rise from, forexample, room temperature to 40° C., to a heat treatment temperature ata temperature rise rate of 0.2° C./min to 1° C./min. The mixturesolution which has undergone the heat treatment for 24 hours or less iscooled to 60° C. or less within 2 hours. Through the above processes, aabrasive particle having a plurality of auxiliary particles 20 formed onthe surface of the mother particle 10 and having a primary particlediameter of 90 nm or less is formed as shown in the schematic view ofFIG. 8A and the photograph of FIG. 8B. Meanwhile, the auxiliary particle20 may be grown and formed to a predetermined size after a nucleus isformed on the surface of the mother particle 10. That is, the auxiliaryparticle is grown after nucleus is formed in the course of temperaturerise to the heat treatment temperature. For example, when the heattreatment is conducted at a temperature of 80° C., nucleus of theauxiliary particle 20 is formed on the surface of the mother particle 10at temperatures rising to 60° C., and is grown during a temperature riseperiod from 60° C. to 80° C., so that the auxiliary particle 20 having apredetermined size is formed. After the auxiliary particle 20 is formedon the surface of the mother particle 10, the auxiliary particle 20 isrigidly bonded to the surface of the mother particle 10 by a heattreatment within 24 hours. That is, the bonding force between the motherparticle 10 and the auxiliary particle 20 may be adjusted according tothe heat treatment time. For example, when the heat treatment time islengthened, the bonding force between the mother particle 10 and theauxiliary particle 20 increases, and when the heat treatment time isshortened, the bonding force between the mother particle 10 and theauxiliary particle 20 decreases. When the bonding force between themother particle 10 and the auxiliary particles 20 is weak, the auxiliaryparticles 20 may be detached from the mother particle 10 during thepolishing process. Therefore, it is preferable that the heat treatmentbe conducted for a sufficient time such that the mother particle 10 andthe auxiliary particles 20 strongly bond to each other. However, whenthe heat treatment time is too long, since the productivity is reduced,it is preferable that the heat treatment time be within 2 hours to 24hours. Also, the size of the auxiliary particles 20 may be adjustedaccording to the heat treatment temperature. That is, when the heattreatment temperature is high, the size of the auxiliary particles 20may increase. For example, at a temperature of 60° C., the nucleus ofthe auxiliary particle 20 is formed but is not grown, so that the sizeof the auxiliary particle 20 is not increased, and at a temperatureabove 60° C., the nucleus is grown, so that the size of the auxiliaryparticle 20 abruptly increases as the temperature rises. However, whenthe heat treatment temperature is too high, the size of the auxiliaryparticles 20 becomes too large, so that a new mother particle 10 may beformed. Therefore, it is preferable that the heat treatment be conductedat a temperature higher than 60° C. and not higher than 100° C.

In order to grow the size of the auxiliary particles 20 formed on thesurface of the mother particle 10, the growing process of the auxiliaryparticles 20 may be conducted at least one time (S300). For example, ina state that the atmosphere of inert gas is maintained, the alkalinesolution is further added to the mixture solution in which the abrasiveparticle the mother particle 10 and the auxiliary particles 20 formed onthe surface of the mother particle 10 is mixed, and stirring isconducted for a time of 5 hours or less, and a cerium aqueous solutionis prepared by mixing cerium and deionized water at a mixing ratio of2:1 to 4:1, and is then heated from room temperature to 40° C. to atemperature of 100° C. or lower at a temperature rise rate of 0.2°C./min to 1° C./min to perform heat treatment for a time of 24 hours orless. The mixture solution which has been subject to the heat treatmentis cooled to room temperature within 2 hours. Through the aboveprocesses, a abrasive particle having a plurality of auxiliary particles20 formed on the surface of the mother particle 10 and having a primaryparticle diameter of 100 nm or less is formed as shown in the schematicview of FIG. 9A and the photograph of FIG. 9B. That is, by repeating thegrowing process of the auxiliary particles 20, the size of the auxiliaryparticles 20 increases, so that the auxiliary particles 20 contact eachother or overlap each other.

As described above, in the case of the mother particle, when the mixturesolution of the precursor aqueous solution and the diluted alkalinesolution is heated at a proper temperature rise rate in a proper heattreatment temperature range, the cerium salt in the mixture solutionreacts to create a fine nucleus of ceria, i.e., cerium oxide (e.g.,CeO₂, Ce₂O₃), and a crystal is grown from the fine nucleus and ismanufactured to a crystal particle having a few nm to a few hundred nm.The crystal nucleation is mainly performed in an initial temperaturerise period, and the crystal growth is mainly conducted in a nexttemperature rise period. Also, in the case of the auxiliary particle,when a solution containing a cerium salt is added to a solutioncontaining the mother particle and the mixture solution is heated at aproper temperature rise rate to a proper temperature, the cerium salt isattached on a surface of the mother particle in the course oftemperature rise to create a nucleus of the auxiliary particle, and thenucleus of the auxiliary particle is grown and is then manufactured tothe auxiliary crystal particle. At this time, similarly to themanufacturing of the mother particle, the crystal nucleation is mainlyperformed in an initial temperature rise period, and the crystal grow ismainly performed in a next temperature rise period. Also, since thenucleus of the auxiliary particle is preferentially created on an edgewhere crystal faces of the mother particle meet, the auxiliary particleis grown centered on the edge of the mother particle.

As described above, the photographs of the abrasive particle includingthe mother particle 10 and the auxiliary particles 20 formed on thesurface of the mother particle 10 according to the present disclosureand the existing dry and wet ceria particles are shown in FIG. 10 forcomparison of shape. That is, FIGS. 10A and 10B are photographs of theexisting dry and wet ceria particles and FIG. 10C is the photograph ofthe abrasive particle according to the present disclosure. As shown inFIG. 10A, since the dry ceria particle is angular in shape of crystalparticle and has a wide particle diameter distribution, the applicationof the dry ceria particle to the CMP process for NAND flash memorydevices inevitably generates micro scratches in the polysilicon layer asshown in FIG. 1. Also, as shown in FIG. 10B, since the wet ceriaparticle has a polyhedral structure and is large in size, theapplication of the wet ceria particle to the CMP process for NAND flashmemory devices inevitably generates micro scratches in the polysiliconlayer as shown in FIG. 2. However, as shown in FIG. 10C, since theabrasive particle according to the present disclosure is small in sizeand does not have sharp crystal faces compared with the existing wetceria particle, although the abrasive particle is applied to the CMPprocess for NAND flash memory devices as shown in FIG. 11, a microscratch is not generated in the polishing layer. Also, as seen from theXRD graph of FIG. 12, the ceria abrasive particle according to thepresent disclosure has almost the same crystallinity as the existing dryand wet ceria particles. Therefore, it may be understood that the ceriaabrasive particle according to the present disclosure has a strengththat may be used as an abrasive particle in a CMP process forplanarizing a device isolation layer.

FIG. 13 is a graph showing a size distribution of auxiliary particlesaccording to temperature in the course of temperature rise to a heattreatment temperature, and FIG. 14 shows photographs of abrasiveparticles at respective temperatures. As shown in FIGS. 13 and 14, theaverage particle diameter of the auxiliary particles at 30° C. is about3.661 nm, the average particle diameter of the auxiliary particles at40° C. is about 3.717 nm, the average particle diameter of the auxiliaryparticles at 50° C. is about 3.718 nm, and the average particle diameterof the auxiliary particles at 60° C. is about 3.574 nm. That is,although the temperature rises from 30° C. to 60° C., the auxiliaryparticles 20 are not almost grown. This is because the nucleus of theauxiliary particle 20 is created but is not further grown. However, whenthe temperature exceeds 60° C., the average particle diameter of theauxiliary particle 20 is abruptly grown, and when the temperature risesto 70° C., the average particle diameter of the auxiliary particle 20increases to 14.632 nm, and when the temperature rises to 80° C., theaverage particle diameter of the auxiliary particle 20 increases to20.843 nm. This is because the nucleus of the auxiliary particle 20 isabruptly grown from the temperature exceeding 60° C. Therefore, in thecase of the abrasive particle according to the present disclosure, itmay be seen that the size of the auxiliary particle 20 abruptlyincreases in a predetermined temperature range in the course oftemperature rise.

FIGS. 15 and 17 are a graph and a photograph showing a size distributionof auxiliary particles according to heat treatment temperature of thepresent disclosure. That is, FIG. 15 shows the size of the auxiliaryparticle when the heat treatment is performed at 60° C., FIG. 16 showsthe size of the auxiliary particle when the heat treatment is performedat 70° C., and FIG. 17 shows the size of the auxiliary particle when theheat treatment is performed at 80° C. As shown in FIG. 15, when the heattreatment is performed at 60° C., the auxiliary particle has a sizedistribution in a range of about 9 nm to about 17 nm, and has a maximumdistribution at about 12 nm. Also, in this case, the average particlediameter of the auxiliary particle is about 11.833 nm. As shown in FIG.16, when the heat treatment is performed at 70° C., the auxiliaryparticle has a size distribution in a range of about 7 nm to about 18nm, and has a maximum distribution at about 11 nm. Also, in this case,the average particle diameter of the auxiliary particle is about 12.375nm. As shown in FIG. 17, when the heat treatment is performed at 80° C.,the auxiliary particle has a size distribution in a range of about 14 nmto about 35 nm, and has a maximum distribution at about 23 nm. Also, inthis case, the average particle diameter of the auxiliary particle isabout 24.533 nm. It may be seen from these results that when the heattreatment temperature is high, the size of the auxiliary particleincreases and the auxiliary particle has a wide size distribution.

A polishing slurry may be manufactured by mixing, in a dispersing agent,the abrasive particles including the mother particle 10 and theplurality of auxiliary particles 20 formed on the surface of the motherparticle 10 and manufactured by the above-described method. Also, apolishing accelerating agent, a pH adjusting agent, and the like may befurther mixed.

The abrasive particle includes a ceria mother particle and a pluralityof ceria auxiliary particles formed on a surface of the ceria motherparticle as described above, and may be contained in an amount of 0.1 wt% to 5 wt % and preferably 0.25 wt % to 2 wt % in the polishing slurrybased on the solid component. In this regard, when the abrasive particleis contained in an amount of 0.1 wt % or less, the polishing rate is toolow, and when the abrasive particle is contained in an amount of 5 wt %or more, the polishing rate is too high, so that a target layer to bepolished may be overpolished.

The polishing accelerating agent may include an cationic low molecularpolymer, an cationic high molecular polymer, a hydroxylic acid, or anamino acid that may convert the surface potential of the abrasiveparticle to minus potential. For example, the cationic low molecular andhigh molecular polymers may include at least one of an oxalic acid, acitric acid, a polysulfonic acid, a polyacrylic acid, a polymethacrylicacid (Darvan C-N), copolymeric acids thereof, or salts thereof. Also,the hydroxylic acid may include at least one of a hydroxylbenzoic acid,an ascorbic acid, or salts thereof. The amino acid may include at leastone of a picolinic acid, a glutaminic acid, a tryptophan acid, anaminobutylic acid, or salts thereof. The polishing accelerating agentmay be contained in an amount of 0.01 wt % to 0.1 wt %, and preferably0.02 wt % to 0.06 wt % based on 1 wt % of the abrasive particle. Whenthe amount of the polishing accelerating agent is less than 0.01 wt %based on the weight of the abrasive particle, the dispersion stabilityis deteriorated, and when the amount of the polishing accelerating agentexceeds 0.1 wt %, the polishing of the target layer to be polished maybe suppressed. Therefore, the weight percentage of the polishingaccelerating agent may be adjusted such that the dispersion stability isenhanced and the polishing is not suppressed.

The pH of the polishing slurry may be adjusted to 4 to 9, preferably 5to 9 by using a pH adjusting agent. When the pH of the polishing slurryis 4 or less, the dispersion stability is deteriorated, and when the pHof the polishing slurry is 9 or higher, the polishing rate of thepolishing stop layer, for example, the polysilicon layer sharplyincreases due to strong alkalinity.

As described above, since the abrasive particle according to anembodiment of the present disclosure is provided with the plurality ofauxiliary particles 20 formed on the surface of the mother particle 10,the abrasive particle may decrease the sharp crystal faces of the motherparticle 10 to the maximum extend. Therefore, the abrasive particle maysuppress the occurrence of micro scratches in the polishing stop layer,for example, the polysilicon layer underlying the target layer to bepolished to the maximum extent, thereby enhancing the device reliabilityand productivity. A method of manufacturing a semiconductor device byusing the polishing slurry containing abrasive particles according to anembodiment of the present disclosure will be described with reference toFIGS. 18 to 20.

Referring to FIG. 18, a tunnel insulating layer 110 is formed on asubstrate 100 and a conductive layer 120 is then formed on the tunnelinsulating layer 110. The substrate 100 may be selected from varioussubstrates used in manufacturing semiconductor devices, and may be, forexample, a silicon substrate. The tunnel insulating layer 110 may beformed by using an oxide layer (SiO₂), a nitride layer (Si₃N₄), or thelike, and may be formed in a single layer structure or a structurehaving at least two layers. In this regard, the insulating layer 110 maybe formed in a thickness that enables tunneling of carriers. Also, theconductive layer 120 may be used as a floating gate of a NAND flashmemory device, and may be formed by using a polysilicon layer.

Referring to FIG. 19, predetermine regions of the conductive layer 120,the tunnel insulating layer 110 and the substrate 100 are etched to apredetermined depth of the substrate 100 to form a plurality oftrenches. An insulating layer 130 is formed such that the trenches arefilled. The insulating layer 130 may be formed of an oxide-basedmaterial, for example, at least one of a borophosphosilicate glass(BPSG) layer, a phosphosilicate glass (PSG) layer, a high density plasma(HDP) layer, a tetra ethyl ortho silicate (TEOS) layer, an undopedsilica glass (USG) layer, a plasma enhanced tetra ethyl ortho silicateglass (PETEOS) layer, and a high aspect ratio process (HARP) layer.Also, the insulating layer 130 may be formed by a physical vapordeposition (PVD) method, a chemical vapor deposition (CVD) method, ametal organic chemical vapor deposition (MOCVD) method, an atomic layerdeposition (ALD) method, or an AL-CVD method in which the CVD method andthe ALD method are combined. Meanwhile, a liner oxide layer may beformed on inner side surfaces of the trenches by oxidizing the substrate100 prior to filling the trenches with the insulating layer 130.

Referring to FIG. 20, the substrate 100 in which the insulating layer130 is filled in the trenches is loaded in a CMP apparatus and then theinsulating layer 130 is polished by using a polishing slurry containingthe abrasive particles according to an embodiment of the presentdisclosure. That is, the insulating layer 130 is polished by using apolishing pad of a polishing apparatus and the polishing slurry untilthe conductive layer 120 is exposed. Also, for sufficient polishing, thepolishing may be further conducted for a predetermined time after theconductive layer 120 is exposed. In this regard, the polishing selectionratio of the insulating layer 130 to the conductive layer 120 is 10:1 to50:1. Thus, a plurality of device isolation layers 140 are formedbetween the conductive layers 120.

Although not shown in the drawings, a second conductive layer, such as apolysilicon layer or the like may be formed on the substrate in whichthe device isolation layers are formed, and then patterned to form afloating gate, and a dielectric layer and a third conductive layer maybe formed on the resultant substrate and then patterned to form acontrol gate. Thus, a NAND flash memory device in which the floatinggate and the control gate are stacked may be manufactured.

Example Manufacturing of Abrasive Particle

An abrasive particle including a mother particle and a plurality ofauxiliary particles formed on a surface of the mother particle accordingto an embodiment of the present disclosure was manufactured as follows.A cerium(III) salt and deionized water were mixed at a mixing ratio of2:1 to 4:1—for example, 1 kg to 4 kg of cerium(III) salt and 0.25 kg to2 kg of deionized water to prepare a cerium(III) aqueous solution, and acerium(IV) salt and deionized water were mixed at a mixing ratio of1:500 to 1:3000—for example, 1 g to 3 g of cerium(IV) salt and 0.5 kg to9 kg of deionized water to prepare a cerium(IV) aqueous solution. Thecerium(IV) aqueous solution and a nitric acid were mixed at a mixingratio of 1:1 to 100:1—for example, 1 kg to 5 kg of the cerium(IV)solution and 0.1 kg to 5 kg of the nitric acid, to prepare a cerium(IV)mixture solution. Also, the cerium(III) aqueous solution and thecerium(IV) mixture solution were mixed to prepare a cerium mixturesolution. Further, ammonia and deionized water were loaded at a mixingratio of 1:2 to 1:10—for example, 1 kg to 5 kg of ammonia and 1 kg to 50kg of deionized water in a reaction container in an inert atmosphere andthen stirred to prepare an alkaline aqueous solution. In a state thatthe cerium mixture solution was put in the reaction container and thenstirred while maintaining the inert atmosphere, the cerium mixturesolution was heated from room temperature to 100° C. or lower—forexample, 70° C. to 90° C. to perform a heat treatment for a time periodof 8 hours or less—for example, 1 hour to 4 hours. By performing theheat treatment as above, a mother particle mixture solution in which aprotrusion is not introduced on a surface thereof was prepared.

Thereafter, the ceria particle mixture solution was cooled to atemperature of 60° C. or lower—for example, 20° C. to 40° C., and theceria particle mixture solution and ammonia were put in a reactioncontainer, mixed at a mixing ratio of 10:1 to 2:1—for example, 8 kg to100 kg of the ceria particle mixture solution and 10 kg to 4 kg ofammonia, and then stirred for a few minutes to a few ten minutes in aninert atmosphere. Then, a secondary cerium mixture solution in which 1kg to 4 kg of a cerium(III) salt, 1 kg to 4 kg of a cerium(IV) salt, 1kg to 9 kg of deionized water and 0.1 kg to 5 kg of a nitric acid weremixed was added to the ceria mixture solution to which ammonia wasadded, stirred, and heated to 100° C. or lower—for example, 70° C. to90° C. to perform a heat treatment for 8 hours or less—for example, 1hour to 4 hours. By completing the heat treatment as above, a particlemixture solution in which a primary auxiliary particle having aprojection shape is formed on a surface of the mother particle wasprepared.

Thereafter, the ceria particle mixture solution in which the primaryauxiliary particle is formed was cooled to a temperature of 60° C. orlower—for example, 20° C. to 40° C., and the ceria particle mixturesolution and ammonia were put in a reaction container, mixed at a mixingratio of 10:1 to 2:1—for example, 8 kg to 100 kg of the ceria particlemixture solution and 10 kg to 4 kg of ammonia, and then stirred for afew minutes to a few ten minutes in an inert atmosphere. Then, atertiary cerium mixture solution in which 1 kg to 4 kg of a cerium(III)salt, 1 kg to 4 kg of a cerium(IV) salt, 1 kg to 9 kg of deionized waterand 0.1 kg to 5 kg of a nitric acid were mixed was added to the ceriamixture solution to which ammonia was added, stirred, and heated to 100°C. or lower—for example, 70° C. to 90° C. to perform a heat treatmentfor 8 hours or less—for example, for 1 hour to 4 hours. By completingthe heat treatment as above, a particle mixture solution in which asecondary auxiliary particle having a projection shape is formed on asurface of the mother particle was prepared.

The particle mixture solution in which the secondary auxiliary particleis formed on the surface of the mother particle was cooled to roomtemperature to adjust pH of the mixture solution to an acidic pH of 4 orless, thereby completing the reaction. The mixture solution of whichreaction was completed was left in room temperature to deposit the ceriaparticles having projections on a surface thereof, then deposition andwashing using deionized water were repeated a few times, and thencentrifugation of the mixture solution was performed to finally obtainparticles.

Comparison Between Example and Comparative Example

Deionized water was added to a ceria suspension containing ceriaabrasive particles having sharp crystal faces of a polyhedral structureaccording to Comparative Example to dilute the ceria suspension, and anitric acid (HNO₃) or ammonia (NH₄OH) was added to adjust the pH of theceria suspension to 4, 5, and 6. These resultant solutions weresufficiently stirred to prepare polishing slurries according tocomparative examples.

Also, deionized water was added to a ceria suspension containing ceriaabrasive particles having a plurality of auxiliary particles formed on asurface of the mother particle manufactured by the above-describedmethod to dilute the ceria suspension, and Darvan C-N was added and thena nitric acid (HNO₃) or ammonia (NH₄OH) was added to adjust the pH ofthe ceria suspension to 4, 5, and 6 These resultant solutions weresufficiently stirred and then ultrasonicated to prepare polishingslurries according to Inventive Examples.

Then, polishing processes were conducted by using the polishing slurriesaccording to Comparative Examples and the polishing slurries. POLI-300(G&P) was used as a polishing apparatus, and IC 1000/Suba IV CMP pad(Dow chemical) was used as a polishing pad. Also, the falling pressureof the polishing pad was set to 6 psi and the rotational speeds of atable and a spindle were all set to 70 rpm. Under such conditions, thepolishing slurries according to Comparative Examples and Examples weresupplied at a flow rate of 100 ml/min to polish a 250 nm thick PETEOSlayer formed on a 75 nm thick polysilicon layer for 60 seconds. Thepolishing results according to Comparative Examples and Examples areshown in Table 1. Also, the shapes of the abrasive particles accordingto Comparative Examples and Examples are shown in the photographs ofFIG. 22. FIG. 23 is a graph showing size distributions of the motherparticle manufactured according to an embodiment, a particle includingprimary auxiliary particles, and a particle having secondary auxiliaryparticles.

TABLE 1 Comparative Example Example Shape Polyhedron Nano embossingPrimary particle diameter (nm) 78.58 77.25 Secondary particle diameter(nm) 157.5 157.4 Zeta Potential (mV) 46.58 −50.02 PETEOS polishing rate(Å/min) 1131 1531 Adding of Polysilicon Polishing rate of 472 680 Stopadditive PETEOS (Å/min) Polishing rate of <20 <20 Polysilicon (Å/min)Thickness of Residual 74.4 ± 0.9 73.8 ± 1.4 Polysilicon (nm)

First, as shown in FIG. 21, it may be seen that the abrasive particlesaccording to Comparative Examples have a polyhedral structure and sharpcrystal faces. However, as shown in FIG. 22, it can be seen that theabrasive particles according to Examples of the present disclosure havea nano-embossing structure in which projection-shaped auxiliaryparticles are formed on a surface of the mother particle. Also, as shownin FIG. 23, the mother particle (A) has a size distribution in a rangeof about 12 nm to about 150 nm, and has a maximum distribution at about32.68 nm. The particle (B) including primary auxiliary particles has asize distribution in a range of about 8 nm to about 150 nm, and has amaximum distribution at about 54.36 nm. Also, the particle (C) includingsecondary auxiliary particles has a size distribution in a range ofabout 17 nm to about 150 nm, and has a maximum distribution at about77.25 nm. Meanwhile, as shown in Table 1, the ceria abrasive particleshaving the polyhedral structure according to Comparative Examples andthe ceria abrasive particles having the nano embossing structureaccording to Inventive Examples have almost similar primary andsecondary particle diameters. That is, the abrasive particles accordingto Comparative Examples have a primary particle diameter of 78.58 nm anda secondary particle diameter of 157.5 nm, and the abrasive particlesaccording to Inventive Examples have a primary particle diameter of77.25 nm and a secondary particle diameter of 157.4 nm. Herein, theprimary particle diameter indicates an average particle diameter of theceria abrasive particles, and the secondary particle diameter indicatesan average particle diameter when the ceria particles are mixed in theslurry. However, the ceria abrasive particles according to ComparativeExamples have a surface Zeta potential of 46.58 mV, and the ceriaabrasive particles according to Examples have a surface Zeta potentialof −50.02 mV that is opposite in polarity to the surface Zeta potentialof Comparative Examples. Also, in case of oxides, the polishing rate ofthe slurry according to Comparative Examples was 1,131 Å/min, and thepolishing rate of the slurry according to Inventive Examples was 1,531Å/min, and it can be seen from these results that the polishing rate ofthe inventive slurry is more excellent than that of the slurry accordingto Comparative Examples. Also, even in case a polysilicon polishing stopadditive was added, the oxide polishing rate of the slurry according toInventive Examples was 680 Å/min and the oxide polishing rate of theslurry according to Comparative Example was 472 Å/min, and it can beseen from these results that the polishing rate of the inventive slurryis more excellent than that of the slurry according to ComparativeExamples. Meanwhile, from comparison results of TEM images after patternCMP shown in FIGS. 24 and 25, it may be seen that there are noremarkable differences in dishing, thickness of residual polysilicon, orthe like. However, in the case of the ceria slurry according toComparative Example, many micro scratches viewed as stain occurred asshown in FIG. 26, but in the case of the ceria slurry according toInventive Example, micro scratches did not occur in a polysilicon layeras shown in FIG. 27. Resultantly, compared with the ceria abrasiveparticles according to Comparative Examples, the ceria abrasiveparticles according to Inventive Example may enhance the polishing rateof oxides as well as decreasing the occurrence of micro scratches in theunderlying polysilicon layer.

According to the embodiments of the present disclosure, since theabrasive particle includes a mother particle having a polyhedralstructure, and a plurality of auxiliary particles provided on a surfaceof the mother particle, the abrasive particle may decrease sharp crystalfaces of the mother particle to the maximum extent. Also, a polishingslurry may be manufactured by using such abrasive particles, and themanufactured polishing slurry may be used to polish an upper oxide-basedmaterial layer in a process of manufacturing 20 nm or less NAND flashmemory devices in which a polysilicon layer used as a floating gate isused as a polishing stop layer.

Therefore, the occurrence of micro scratches in the polysilicon layerunderlying the target layer to be polished may be suppressed to themaximum extent, and thus a change in threshold voltage may be prevented,thereby enhancing the device reliability. Furthermore, the polishingrate of an oxide layer may be improved and the polishing selection ratioof an oxide layer and a polysilicon layer may be improved, thusdecreasing the polishing process time to enhance the productivity.

Although the abrasive particle, the polishing slurry, and the method ofmanufacturing a semiconductor device using the same have been describedwith reference to the specific embodiments, they are not limitedthereto. Therefore, it will be readily understood by those skilled inthe art that various modifications and changes can be made theretowithout departing from the spirit and scope of the present inventiondefined by the appended claims.

What is claimed is:
 1. A method of manufacturing a polishing slurrypolishing a workpiece, wherein an abrasive particle which polishes theworkpiece and has a plurality of protrusions protruded outward isdispersed in a dispersing agent.
 2. The method of claim 1, wherein theabrasive particle comprises polyhedral crystal faces, and the protrusionis formed from an edge where at least two of the polyhedral crystalfaces meet.
 3. The method of claim 2, wherein the auxiliary particle tothe mother particle is formed at a size ratio of approximately 100:1 toapproximately 5:1.
 4. The method of claim 3, wherein the abrasiveparticle is contained in an amount ranging from approximately 0.1 wt %to approximately 5 wt % based on a solid component.
 5. The method ofclaim 1, further comprising adding a polishing accelerating agent,wherein the polishing accelerating agent comprises a cationic lowmolecular weight polymer, a cationic high molecular weight polymer, ahydroxylic acid, and an amino acid, which convert a surface potential ofthe abrasive particle to a minus potential.
 6. The method of claim 5,wherein the polishing accelerating agent is contained in an amount ofapproximately 0.01 wt % to approximately 0.1 wt % based on 1 wt % of theabrasive particle.
 7. The method of claim 6, wherein the cationic lowmolecular and high molecular polymers comprise at least one of an oxalicacid, a citric acid, a polysulfonic acid, a polyacrylic acid, apolymethacrylic acid (Darvan C-N), copolymeric acids thereof, or saltsthereof, the hydroxylic acid comprises at least one of a hydroxylbenzoicacid, an ascorbic acid, or salts thereof, and the amino acid comprisesat least one of a picolinic acid, a glutaminic acid, a tryptophan acid,an aminobutylic acid, or salts thereof.
 8. The method of claim 1,further comprising adding a pH adjusting agent adjusting pH of theslurry, wherein the pH of the slurry is maintained in a range of 4 to 9by the pH adjusting agent.
 9. The method of claim 5, further comprisingadding a pH adjusting agent adjusting pH of the slurry, wherein the pHof the slurry is maintained in a range of 4 to 9 by the pH adjustingagent.